Method and composition for sealing anodized aluminum surfaces

ABSTRACT

PROCESS AND COMPOSITION FOR SEALING ANODIZED ALUMINUM SURFACES. THE COMPOSITION CONTAINS 35-60% NICKEL ACETATE OR COBALT ACETATE; 35-60% OF THE AMMONIUM SALT OF NAPHTHALENE SULFONIC ACID, AND MINOR QUANTITIES OF A CONDENSATION PRODUCT OF OCTYL PHENOL WITH ETHYLENE OXIDE AND MALIC ACID. THE COMPOSITION IS APPLIED IN HOT AQUEOUS SOLUTION TO THE ALUMINUM SURFACES TO BE SEALED.

United States Patent ()ffice' 3,647,649 Patented Mar. 7, 1972 ABSTRACT OF THE DISCLOSURE Process and composition for sealing anodized aluminum surfaces. The composition contains 35-60% nickel acetate or cobalt acetate; 35-60% of the ammonium salt of naphthalene sulfonic acid, and minor quantities of a condensation product of octyl phenol with ethylene oxide and malic acid. The composition is applied in hot aqueous solution to the aluminum surfaces to be sealed.

This invention relates to a method and composition for sealing anodized surfaces of aluminum and aluminumbase alloys. More particularly, it relates to a method and composition for sealing such surfaces to obtain a harder, more abrasive-resistant surface of greater resistivity while eliminating or minimizing smut formation.

It is conventional to seal anodized aluminum surfaces in order to increase the resistance of the anodized coating to stains and corrosion, to increase the durability of any color produced in the coating, and to increase the resistance of the surface to abrasion and wear. Current sealing methods include treatment with hot water and with solutions of certain hydrolyzable metal salts.

Treatment with hot or boiling water is typically used for clear (undyed) surfaces. This method requires water which is free of impurities and ideally is conducted with deionized water, For use with colored anodized coatings, a sealing bath in common use comprises a solution of a hydrolyzable metallic salt, typically nickel acetate or cobalt acetate. Sealing with such a bath sets the dye, minimizes color bleeding and improves the permanence of the color. Nickel or cobalt acetate treatment, however, has the disadvantage that it produces a cloudy or filmy coating on the surface of the sealed material. This coating, referred to in the trade as smut, is particularly serious with dark shades and necessitates an additional step in the processing procedure to remove the filmy layer by mechanically butting or polishing the aluminum surface. The necessity for smut removal represents an added cost in the processing of aluminum articles, since each piece must be handled individually. In addition, in the case of complicated shapes it may be impossible to remove the smut effectively by mechanical means.

In accordance with the invention, there is provided a sealing method which eliminates or minimizes the formation of smut on the sealed aluminum surfaces while at the same time improving the wear and corrosion resistance of the treated surfaces over those obtainable by the sealing methods heretofore known. In addition, the sealing bath of the invention can be prepared with ordinary tap water and has a much improved service life compared with baths heretofore used.

The method of the invention is a variant of the hydrolyzable metal salt sealing technique, in that it employs as a sealing bath a solution of nickel acetate or cobalt acetate. The superior performance of the sealing bath of the invention, however, is due to a novel combination of additives, namely, the ammonium salt of naphthalene sulfonic acid, two specific wetting agents, and malic acid.

The sealing bath of the invention is prepared by dissolving in water a solid mixture having the following composition:

Concentration, weight percent Ingredient Broad Preferred Nickel acetate, cobalt acetate, or mixtures thereof. 35-60 4250 Ammonium salt of naphthalene sulionlc acid (d 1spersant)' 35-60 42-50 Sodium lauryl sulfate (wetting agent) 0. 03-0. 3 0. 05-0. 15 Octyl phenoxy polyethoxy ethanol (wetting agent) 0. 1-1. 0 0. 2-0. 5 Make acid (bufier) 0. 5-4. 0 1. 0-2. 0

The octyl phenoxy polyethoxy ethanol referred to above, and which is contemplated for use in the invention, is the product produced by the condensation of one mole of isoor n-octyl phenol with about 12-13 moles of ethylene oxide.

A particularly preferred embodiment of the sealing composition of the invention contains, on a water-free basis, about 49% of nickel acetate, cobalt acetate or mixtures thereof; about 49% of the ammonium salt naphthalene sulfonic acid; about 0.1% of sodium lauryl sulfate; about 0.25% of octyl phenoxy polyethoxy ethanol; and about 1.5% of malic acid.

The sealing composition of the invention is used by dissolving it in water at a concentration of about 2-16 grams per liter, preferably about 2.5-10 grams per liter, and optimally about 5-8 grams per liter. The. sealing solution is heated to a temperature of about F. to the boiling point of the solution and preferably about 185- 205 F. The pH of the solution is adjusted as necessary with a suitable acid or base, such as acetic acid, ammonium hydroxide or sodium hydroxide, to achieve a value within the range of about 5.2-5.8 and preferably about 5.4-5.6. Contact of the sealing solution with the surfaces to be treated is maintained in the conventional manner for about 3-20 minutes and preferably about 5-10 minutes. The manipulative aspects of the sealing operation are not critical and any of the methods which have been used in the past may be employed with the novel baths of the invention.

The method and composition of the invention are illustrated by the following examples.

EXAMPLE I A sealing bath is prepared by dissolving in city (tap) water about 4.4 grams per liter of a composition consisting of 49 parts by weight of nickel acetate, 49 parts by weight of the ammonium salt of naphthalene sulfonic acid, 0.25 part by weight of the condensation product of one mole of isooctyl phenol with about 12-13 moles of ethylene oxide, 0.08 part by weight of sodium lauryl sulfate, and 1.5 parts by weight of malic acid. The pH of the resulting solution is adjusted with acetic acid to a value of 5.4. This solution, maintained at a temperature of about 192 F., is used to seal an Anoclad 11 sheet having a 215 R1 anodic finish for about 10 minutes. The sealed sheet is essentially smut free. In comparison with control samples of the same aluminum sheet sealed in boiling deionized water for 30 minutes at a pH of about 6.4, the sheets sealed in accordance with the invention show greater resistance to acid dissolution and equivalent surface resistivity.

EXAMPLE II A sealing bath is prepared using the same ingredients and concentrations as those of Example I, except that deionized water is used in place of city water. The use of deionized water results in sealed samples having slightly lower acid dissolution rate and slightly higher resistance values than samples sealed with the solution of Example I. The aluminum surfaces sealed with the solution are again essentially smut free.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understooditherefrom,"=as modifications will be obvious to those skilled in the art. 1 I

1. A water-soluble composition for sealing anodized aluminum comprising about 35-60% by weight of nickel acetate, cobalt acetate or mixtures thereof; about 35-60% by weight of the ammonium; salt 16f naphthalene sulfonic acid; about 0.03-0.'3% byweight ofsodium laury-l-sulfate; about 01-10% by weight'of the condensation'productof one mole of octyl phenol with about 12-13 moles of ethylene oxide; and about 0.5-4.0% by weight of malic acid.

2. A composition in accordance with claim 1 which contains about 42-50% by weight of nickel acetate, cobalt acetate, or mixtures thereof; about 4250% by weight of the ammonium salt of naphthalene sulfonic acid; about 0.05-0.15% by weight of sodium lauryl sulfate; about 02-05% by weight of the condensation product of one mole of octyl phenol with about 12-13 moles of ethylene oxide; and about 1.0-2.0% by weight of malic acid.

3. A composition in accordance with claim 1 which contains about 49% by weight of nickel acetate, cobalt acetate, or mixtures thereof; about 49% of the ammonium salt of naphthalene sulfonic acid; about 0.1% by weight of sodium lauryl sulfate; about 0.25% by weight of the condensation product of one mole of octyl phenol with about 12-13 moles of ethylene oxide; and about 1.5% by weight of malic acid.

4. A. bath for sealing anodized aluminum comprising an aqueous solution containing about 2-16 grams per liter of a composition of claim 1.

5. A bath in accordance with claim 4 containing about 5-8 grams per liter of a composition of claim 1.

comprising contacting said anodized surfaces with an aqueous'soluti'on containing about'2-16 grams per liter ofa composition in accordancewith claim 1, said solution having a temperature from'about 185 F. to the boiling point of the solution and a pH within the range of about 5.2-5.8, and maintaining contact-between said aluminum surfaces and said solution for about 3-20 minutes. i

7. The method of claim 6, wherein said solution contains about 5-8 grams per literof a composition in accordance with claim 2, said contact'being maintained for about 5-10 minutes at a temperature of about 185- 205..-F.

8. A method in accordance with claim 6 in which said solution contains about 5-8 grams per liter of a com 6. A method of sealing anodized aluminum surfaces position of claim 3, said contact being, maintained for about 5-10 minutes at a temperature of about -205 F.

9. An aluminum article having an anodized surface, said surface having been scaled by a'process in accordance with the method of claim 6.

References Cited UNITED STATES PATENTS 2,231,373 2/1941 Schenk 204-35 N 3,468,766 9/1969 Lang 204-35 N 3,031,387 4/1962' Deal et al. 204-35 N 3,098,018 7/1963 Kissin et al. 204-35 N 3,012,917 12/1961 Riov et al. 148-6.14 3,171,797 3/1965 Klingenmaier 204-35 N 2,755,239 7/1956. Glauser et al. 204-35 N 3,380,860 4/ 1968 Lipinski 204-35 N JOHN H. MACK, Primary Examiner R. I. FAY, Assistant Examiner US. Cl. X.R.I 148-627; 204-58, 38 A 

